Crystal Set Observations
While trying out the varactor crystal set in the evening
https://wb9kzy.blogspot.com/2024/07/varactor-crystal-set.html
(it was not a good night for listening, t-storms approaching) I noticed a couple of things:
1) My HP 6281a supply was putting out zero volts ! I've mentioned this unit before:
https://wb9kzy.blogspot.com/2022/01/the-hp-6281a-power-supply.html
Oh no ! It was a very warm/humid evening and I had left the supply on continuously for hours. Also, I had placed a digital scale on top of the supply, blocking some of the vent holes. I turned it off and when I retried it this morning it appears to be OK. Must have just been something overheated - I'll find another place to stow that digital scale and I also started using a 9V battery to power the varactors since the current used is very low.
2) The "utility" audio amplifier I've been using with the crystal set sounds distorted. I scoped the output - it appears that there is a problem with the positive going audio - might be a bad chip ?
This amplifier is pre-notebook era for me so no schematics or notes. It uses a 14 pin LM380N audio amplifier chip (same one used in the Ten-Tec Argonaut). There is also an LM317 voltage regulator driven by full wave rectification of a small, shielded power transformer. One unusual thing is a bifilar 88 mH toroid is used between the rectifier and the input to the LM317 as a hum filter ? The toroid is under the duct tape:
Now the decision is whether to attempt repair or just ditch it and build a new amplifier.
Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm
https://wb9kzy.blogspot.com/2024/07/varactor-crystal-set.html
(it was not a good night for listening, t-storms approaching) I noticed a couple of things:
1) My HP 6281a supply was putting out zero volts ! I've mentioned this unit before:
https://wb9kzy.blogspot.com/2022/01/the-hp-6281a-power-supply.html
Oh no ! It was a very warm/humid evening and I had left the supply on continuously for hours. Also, I had placed a digital scale on top of the supply, blocking some of the vent holes. I turned it off and when I retried it this morning it appears to be OK. Must have just been something overheated - I'll find another place to stow that digital scale and I also started using a 9V battery to power the varactors since the current used is very low.
2) The "utility" audio amplifier I've been using with the crystal set sounds distorted. I scoped the output - it appears that there is a problem with the positive going audio - might be a bad chip ?
This amplifier is pre-notebook era for me so no schematics or notes. It uses a 14 pin LM380N audio amplifier chip (same one used in the Ten-Tec Argonaut). There is also an LM317 voltage regulator driven by full wave rectification of a small, shielded power transformer. One unusual thing is a bifilar 88 mH toroid is used between the rectifier and the input to the LM317 as a hum filter ? The toroid is under the duct tape:
Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm
